Glycosaminoglycans: Effect on Muscle Development. The development of muscle cells in both normal and disease states has been of great interest to the developmental biologists. Of particular interest have been questions concerning the signals which can influence the rate of extent of differentiationand the specific order of events that take place. In recent years, molecules of the extracellular matrix have been suggested as possible regulators of development, with changes in composition of the matrix being correlated with differentiation. Recently, our laboratory has performed experiments in which myogenic cells were grown on difference kinds of glycosaminoglycans. Cells grown on chondroitin sulfate appear to differentiate normally, while those grown on hyaluronic acid do not. Since hyaluronic acid has been correlated with proliferation in many other systems, it is important to explore the effects of this compound on myogenesis. The experiments proposed here will utilize tissue culture cells and will be directed toward determining the extent of inhibition of myogenesis by hyaluronic acid. They will also investigate the question of whether the inhibition takes place directly through hyaluronic acid or requires intermediate molecules. The results will be of importance both in studies of regulation of myogenesis itself and in understanding possible regulatory roles of glycosaminoglycans.